Support enums as strings in APIs

[ascott18]

If an enum is annotated with [JsonConverter(typeof(JsonStringEnumConverter))], support it being a string in the API.

The code generation will need to emit a new metadata property on the enum type definition. All other changes will be in coalesce-vue

[ascott18]

This is kind of cursed in the complexity it brings, and nobody is actually yet asking for this.